LONDON — Traveling here on what many regard as the finest urban mass transit system is a reminder of urban transit's possibilities. A week spent in Iffley, a village that my daughter Beth described as Oxford's Mill Valley, demonstrates suburban transit's limitations.

It's regrettable and unnecessary that public transportation has been coupled with the contentious fight over high-density development. That connection likely set back public support for North Bay transit improvements by a decade.

Some prominent high-density housing proponents over-promised and misapplied transit's function. The linkage has been misused to greenwash some lucrative large-scale residential developments. Yet, that's not to ignore that enhanced transit has real benefits even in Marin.

London Transport demonstrates transit's capabilities in a city-centered metropolitan region.

"LT" is a network of efficient, frequent but expensive-to-ride subways and double-decked buses. The capital city's density is such that transit and taxis are effectively the exclusive means of intracity mobility.

London is also home of the world's first suburban railways. They made possible the very concept of suburb. Commuter rail demonstrates that the most effective use of transit in suburbs is moving residents of low-density communities to concentrated central business districts.

Other than New York, no other American or British city has such high density, allowing transit to work so effectively. Recreating that mass in San Francisco or even Chicago or Philadelphia is unrealistic.

To imagine such population concentration in Marin or any other suburban region is preposterous.

Low-density Oxford provides a more Marin model.

Other than the city center, where a dozen blocks are limited to buses, most residents own a personal vehicle.

In Oxford, automobiles are essential to access the town's suburbs. Like Marinites, many Britons prefer a lifestyle in low-density leafy suburbs.

While there's good local bus service, it's most useful to those attending the university or working in the town's center.

There are lessons here for Marin and the Bay Area.

Rail, buses and ferries work well as trunk lines delivering workers from small- and medium-sized suburban communities to central job centers like downtown San Francisco.

Regional planners of the 1980s, aided by San Francisco's political left fearing the city's "Manhattanization," derided this model.

They wrongly believed that if Californians simply lived and worked in suburbia, the jobs-housing balance would be resolved. That turned out to be a model that could never be served by transit. The suburb-to-suburb commute is inherently auto dependent.

We're still paying for that fiasco. The percentage of Bay Area workers in central San Francisco plunged with the rise of large-scale suburban employment.

Planners now need to encourage the old but effective model of San Francisco as the Bay Area's employment center.

The North Bay is doing its part with Sonoma-Marin Area Rail Transit, a commuter rail line designed to bring workers south from Sonoma and northern Marin. Coupled with convenient ferry connections, commuters will enjoy the most efficient and environmentally sensitive travel mode to the region's revitalized employment center.

Trying to urbanize American suburbia is a fool's errand. Densities high enough to justify large-scale transit will never be created no matter how many growth-inducing blockbusters like Corte Madera's Tamal Vista Apartments are built.

The upshot will be the destruction of the quality of life that enticed most of us to places like Marin.

Given the travel imperatives of a mobile, two-income household, intra-suburban transit works well as an alternative, not a substitute, for the auto.

Americans — and the Brits — demand choices. In Marin, good, balanced public policy provides appropriate transit, improves freeways and includes a coherent network of bicycle and pedestrian pathways.

Columnist Dick Spotswood of Mill Valley now shares his views on local politics twice weekly in the IJ. His email address is spotswood@comcast.net.